put a level against the guards to the ground (and make sure its plumb). measure the distance from the level to the existing rim.
then go to https://www.wheel-size.com/size/ford/falcon/ to find the existing size/ offset of your rims.
then go to https://www.willtheyfit.com/ and enter the existing measurements, then the measurements that will make it flush with he guard if you want it flush. adjust for poke, or in a bit, or whatever.
I wouldnt go closer to the strut, and if your increasing rim diameter you might even need to go further away. pop your hand to the the top of the rear of the tyre and feel what kind of clearance you have.

ha ha- that weirdo- whats his name- goeers? would NOT like that... especially if I pass him on his bike...
its pretty much the same car as audi Q7 and Porsche Cayenne- same running gear and underpinnings, but cheaper, so I guess they feel can justify a VW with a 100k + price tag...

yeah theyre nice.
I looked at Q7, range rover discovery 4, range rover sport, Porsche cayenne- but after having my Touareg for 2 years I love it, so it made sense to upgrade.
the other problem I have is can I rock up to renovate someones bathroom in an Audi or a Porsche?

yeah ive still got both cars- selling the black one with whatever rims I dont want.
although maybe I should just get stock 17s to put on the car im selling and put the r line wheels in the garage for when I eventually sell it.
the 21's have brand new pirellis on them...